Concretes formed from hydraulic cements, of which Portland cement is the most common example, are used as structural components in various applications, such as in the formation of roads, bridge deckings, building structures, multi-story automobile storage structures and the like. In order to enhance the properties of the concrete to permit its use in these structures, the material normally is used in combination with iron or steel reinforcing structures therein. These reinforcing metal structures, usually in the form of metal rods or bars, are subjected to attack by the various corrosive elements contained in the concrete, as well as by the application of external corrosive elements to the structure, such as chloride salts and the like, which are commonly used in the removal of ice and snow from roads, bridges, pedestrian walkways and the like. Further, various structures located at coastal installations and the like are subject to corrosive salt attack from the marine environment. The repair and replacement of such structures which have deteriorated due to the effects of such corrosive forces is extensive and in certain instances requires complete replacement of the structure as unsuitable for its intended use.
In attempts to counteract the corrosive effects normally encountered by concrete structures, as discussed above, various corrosion inhibiting agents have been proposed for use as admixtures to be used in their formation.
U.S. Pat. No. 3,210,207 (Dodson et al.) discloses the use of mixes of calcium formate with minor amounts of certain benzoate, nitrite or chromate salts as corrosion inhibitors, to be used as accelerators in cements.
U.S. Pat. No. 3,427,175 (Angstadt et al.) discloses the use of calcium nitrite as an accelerator which partially inhibits corrosion in alite cements. The calcium nitrite may contain minor amounts of sodium nitrite and may be used with calcium chloride and other accelerators.
U.S. Pat. No. 3,801,338 (Whitaker) discloses the use of a mixture of calcium formate and sodium nitrite, optionally with triethanolamine or sodium benzoate, for adding to cement which is to contain metal reinforcement. Improved compressive strength is taught, together with sulfate resistance, and a positive corrosion inhibition effect.
U.S. Pat. No. 3,976,494 (Kudo et al.) discloses a process for inhibiting corrosion of iron or steel placed in cement which comprises adding to the cement a nitrite and an ester of phosphoric acid and/or an ester of boric acid.
U.S. Pat. No. 4,285,733 (Rosenberg et al.) discloses the addition of at least about 2% calcium nitrite to concrete to inhibit the corrosion of metal pieces contained therein.
U.S. Pat. No. 5,262,089 (Bobrowski et al.) discloses an admixture for inhibiting chloride-induced corrosion in steel reinforcing in place in concrete comprises an oil-in-water emulsion wherein the oil phase comprises an unsaturated fatty acid ester and ethoxylated nonyl phenol and the ester of an aliphatic carboxylic acid with a mono-, di- or trihydric alcohol and the water phase comprises a saturated fatty acid, an amphoteric compound, a glycol and a soap. The admixture is added to the concrete prior to placement.
U.S. Pat. No. 4,442,021 (Burge et al.) discloses that corrosion protection of metallic articles within concrete structures can be accomplished by coating the articles with a coating comprising an aqueous suspension of 10-99.99% of hydraulic binding agents, preferably cement or mixtures thereof with latent hydraulic additives, and 0.01-10% corrosion inhibitors. The coating is applied onto the metallic articles intended to be enclosed in concrete structures.